The invention relates to the refining of fatty substances, in particular of oils, in order to selectively free them from most of their free fatty acids.
In the treatment of fatty substances, the removal of free fatty acids is a major step, the aim of which is to lead to oxidation, products with good stability and good organoleptic qualities.
The following process for removal of free fatty acids from fatty substances are known in the art: alkaline refining, refining micelles, steam distillation, liquid/liquid extraction and membrane or chromatographic separation. Among these known methods, only alkaline refining and steam distillation are applied on an industrial scale.
These known methods have disadvantages. For example, some of the disadvantages of alkaline refining are loss of neutral oil by saponification, occlusion of soaps in the neutral oil, elimination of active phenolic compounds and the need to treat the soaps. By way of illustration, a process for refining oils containing fatty acids as impurities by neutralizing the crude oils with an aqueous alkaline solution containing a polyol and separating the purified oils from the soaps formed is known, for example, from FR-A-2321537.
One of the disadvantages of steam distillation is that it takes place at high temperature and under a high vacuum, which causes losses of volatile nutrients, for example tocopherols, undesirable chemical changes, for example formation of trans fatty acids, changes in color and polymerizations.
An object of this invention is to provide an industrially applicable process which selectively and quantitatively removes the fatty acids without exhibiting the above mentioned disadvantages.
The present invention provides a process for removal of free fatty acids from fatty substances or oils. In particular, this process comprises removal of free fatty acids by a controlled neutralization, at a temperature greater than the melting point of the fatty substances, in an aqueous medium containing an alcohol or a polyol. A base is gradually added to the reaction medium so as to maintain the pH at 9-11, which leads to partition of the free fatty acids between a lipid phase and an aqueous phase containing the alcohol or the polyol, that is nonmiscible with the lipid phase. The formation of soaps, which are solubilized progressively in the aqueous phase, produces a shift in the equilibrium and a gradual deacidification of the lipid phase until the pH has stabilized, in that the two phases are separated and in that the deacidified lipid phase is collected, from which the alcohol or the polyol is removed.
In the text which follows, fatty substances will be called xe2x80x9coilsxe2x80x9d for the sake of simplicity.
According to a first embodiment of the process, the controlled neutralization of the fat containing free fatty acids is carried out in a reactor equipped with a pH electrode, with a stirrer and a pH-stat equipped with a burette delivering an aqueous alkaline solution. The pH-stat is connected to the pH electrode so as to provide the alkaline solution as required when a set pH value, for example 9.5, is reached.
The reaction is carried out in the presence of alcohol, in a homogeneous medium with slow stirring, at a temperature greater than the melting point of the fatty substance and less than the azeotropic boiling point of the aqueous-alcoholic mixture, preferably at room temperature. The stirring conditions chosen are such that the lipid phase and the aqueous-alcoholic phase remain separated during the neutralization, which makes it possible to avoid the formation of stable emulsions due to the presence of soaps. The pH electrode is in contact with the aqueous-alcoholic phase alone. In this embodiment, the neutralization lasts for 6 to 20 h depending on the pH chosen for the neutralization, depending on the characteristics of the equipment and depending on the nature of the initial fat. The fat:alcohol volume ratio used is 1:0.5 to 1:2.5.
It is possible to use, as alcohol, a C1-C3 alcohol, preferably ethanol or 2-propanol.
In a preferred embodiment, allowing easier application on an industrial scale, the process according to the invention may be carried out in a heterogeneous medium, with vigorous stirring, in the presence of an alcohol or a polyol at a temperature of 40 to 80xc2x0 C., with a pH of 9-11 and in a simple manner, without using a pH-stat. The quantity of alkali just required for the neutralization is calculated, without excess of alkali, relative to the quantity of free fatty acids present, determined for example by calorimetric titration. The neutralization may be carried out in about 60 min. As polyol, there may be used glycerol, propylene glycol, ethylene glycol or a polyalkylene glycol, in particular a polyethylene glycol, propylene glycol or a polyethylene glycol being preferred, anhydrous or diluted with water. The polyol:fat weight ratio may be, preferably, from 0.5:10 to 1:1.
The advantage of using a polyol is being able to work in conventional plants, that it is not necessary for the plant to be constructed in order to withstand explosions with a device for recovering the solvents.
Regardless of the variant of the process, it is possible to use, as alkali, an aqueous solution of KOH or of NaOH at concentrations of 1 to 40% by weight.
A decisive advantage of the process according to the invention is that, in contrast to conventional refining processes, it is not necessary to add alkali in excess for the neutralization. The weakly acidic phenolic substances are thus preserved and the alkaline hydrolysis of the triacylglycerols avoided.
Furthermore, it is not necessary to know precisely either the quantity of fatty acids present in the fat, or the weight of the fat to be neutralized.